The present invention relates to a process for preparing lactams by cyclizing hydrolysis of amino nitriles with water in the gas phase on metal oxide catalysts.
Lactams are compounds which can be employed in a variety of ways. For example, N-methylpyrrolidone is a versatile solvent and xcex5-caprolactam is an important monomer for polyamide fibers. Caprolactam is prepared industrially by a Beckmann rearrangement of the oxime of cyclohexanone. This reaction results in large amounts of salts, generally sodium sulfate, as byproduct which must be disposed of.
U.S. Pat. No. 2,357,484 discloses a process for preparing amides and lactams from the corresponding nitriles and amines, and the amino nitriles respectively, by gas-phase reaction with water on catalysts with dehydrating properties. Catalysts indicated as usable are, in particular, alumina, silica gel and boric/phosphoric acid.
WO 96/22974 describes a process for preparing lactams by cyclizing hydrolysis of amino nitriles, using alumina catalysts with a specific surface area of xe2x89xa710 m2/g and a pore volume (of pores with a diameter of more than 500 xc3x85) xe2x89xa710 ml/100 g.
U.S. Pat. No. 4,628,085 discloses a process for preparing lactams in the gas phase, where an aliphatic or aromatic amino nitrile and water are brought into contact with a silica-based catalyst with BET surface areas of more than 250 m2/g and pore diameters of less than 20 nm in the presence of hydrogen and ammonia.
The use of metal phosphates, especially aluminum, zirconium, niobium and lanthanum phosphates, as catalysts for preparing lactams in the gas phase from amino nitriles and water is described in EP-A 659 741. These catalysts can also be impregnated with basic alkali metal or alkaline earth metal compositions, with cesium, rubidium and potassium being preferred.
EP-A 748 797 discloses a process for preparing lactams from dinitriles, where the dinitrile is hydrogenated to the amino nitrile, and the amino nitrile is converted into the lactam by cyclizing hydrolysis. Disclosed as catalyst for the cyclizing hydrolysis are molecular sieves such as acidic zeolites, silicates and non-zeolite molecular sieves, metal phosphates and metal oxides or mixed oxides, which are, where appropriate, acidic or amphoteric due to treatment with halogens, ammonium halides or acids such as sulfuric acid or hydrohalic acid.
The disadvantage of the described processes is that the selectivity of the catalysts is inadequate in some cases, which on the one hand makes it difficult to isolate the lactams, and on the other hand leads to poisoning of the catalysts by the byproducts which are formed. It is also desirable to increase the activity of the catalysts.
It is an object of the present invention to provide a process for preparing lactams by cyclizing hydrolysis of amino nitriles which affords them with high selectivity and high space-time yield and, moreover, allows a long useful life of the catalyst.
We have found that this object is achieved by reacting the amino nitriles with water on oxides of the metals of groups 3, 4, 5, 13 and/or 14 of the Periodic Table as catalysts which comprise a phosphate, carbonate, silicate, arsenite, arsenate, antimonite, antimonate or nitrate of said metals and, where appropriate, a metal oxide of groups 6, 7, 8, 9 and/or 10.
The present invention therefore relates to a process for preparing lactams by cyclizing hydrolysis of amino nitriles with water in the gas phase on metal oxide catalysts, wherein the catalysts comprise:
at least one oxide or mixed oxide of the metals of groups 3, 4, 5, 13 and/or 14 of the Periodic Table,
one or more oxides or mixed oxides of metals of groups 6, 7, 8, 9 and/or 10,
at least one carbonate, silicate, phosphate, arsenite, arsenate, antimonite, antimonate and/or nitrate and/or when oxides or mixed oxides of metals of groups 6, 7, 8, 9 or 10 are present, a sulfate of the abovementioned metals.
The numbering of the groups of the Periodic Table in this specification is in accordance with the 1985 IUPAC proposal.
Catalysts preferred according to the invention are compounds of the formula I:
MQa(ROb)cOdxe2x80x83xe2x80x83(I)
in which
M is Zr, Ti, Hf, Sc, Y, La, Ce, V, Nb or Ta, in particular Zr, Ti or Hf, and very especially Zr,
R is P, C, Si, N, As or Sb,
Q is a metal from group 6, 7, 8, 9 or 10,
a is a number from 0 to 10,
b is a number from 0.5 to 5,
c is a number from 0.001 to 0.15, and
d has the magnitude necessary to achieve neutrality of charge.
The catalysts comprise up to five molecules of water per formula unit. If a xe2x89xa70.001, R can also be S.
Catalysts which are particularly preferably used are compounds of the formula I in which
R is P or, if a xe2x89xa70.001, can also be S,
Q is Mn,
a is 0 to 0.1 and very particularly preferably 0 to 0.03, and
c is 0.001 to 0.1 and very particularly preferably 0.01 to 0.1,
and particularly preferred compounds are those in which R is P and Q is Mn.
The catalyst materials can be employed in any suitable form such as, for example, as powder, as chips or else as shaped articles. Examples of shaped articles which are used are extrudates or beads. For the shaping, a binder can be added, such as, for example, Aerosil, potato starch or celluloses, for example Walocel supplied by Wolff-Walsrode AG, these binders not being present in stated formula I. It is likewise possible for the catalyst materials to be applied to a carrier such as, for example, alumina, silica gel, carbon, silicon carbide or silicon nitride. The catalyst is preferably used in the novel process in the form of chips or shaped articles.
The catalyst bed may be mixed with a component to increase the selectivity in amounts of from 0 to 70% by volume. Examples thereof are silicon dioxide, preferably quartz, silicon nitride and silicon carbide.
The catalysts are prepared in a manner known per se and familiar to the skilled worker. The novel catalysts can be obtained, for example, by contacting at least one oxide and/or hydroxide of a metal of groups 3, 4, 5, 13 and/or 14 of the Periodic Table one or more times with suitable phosphates, sulfates, carbonates, silicates, arsenites, arsenates, antimonites, antimonates or nitrates, and then calcining at elevated temperature. Suitable examples are the corresponding salts of metals of groups 3, 4, 5, 13 and 14 of the Periodic Table, the ammonium salts of oxo acids of these metals and, if desired, the salts of the metals of groups 6 to 10 of the Periodic Table, and phosphoric acid, sulfuric acid or nitric acid and their ammonium salts.
The contacting takes place, for example, by adding a solution of the required phosphate, carbonate, silicate, nitrate, arsenite, arsenate, antimonite, antimonate or sulfate, or of the corresponding free acid, to an aqueous suspension of the metal oxide or hydroxide of groups 3, 4, 5, 13 or 14, of the Periodic Table, and then removing the water. This procedure can be repeated. The required components can be brought into contact all at once or in separate steps with the suspension of the metal oxide. In place of the solutions of the abovementioned salts, it is also possible to employ solutions of different salts of these metals in sulfuric acid, phosphoric acid or nitric acid, which is diluted with water where appropriate, as long as the anion of these salts forms a volatile acid with the mineral acid. Suitable salts are thus also the halides and the acetates as long as these are employed in one of the abovementioned acids or in aqueous solutions of these acids.
The components can moreover be converted into a homogeneous solution from which a crude catalyst composition is obtained, for example by evaporation or by addition of a precipitant, and is then converted into the active form of the catalyst by drying and calcination.
A further possible procedure is to spray a molding of the metal oxide, such as pellets, beads, hemispheres or extrudates, with aqueous solutions of suitable salts or the free acids. This procedure can be repeated several times, as a rule carrying out drying steps between the individual impregnation steps.
In a preferred preparation process, the metals or metal oxides are brought into contact with one of the abovementioned free acids in a first step and then, after a drying step, if required, brought into contact with an aqueous solution of a suitable metal salt of groups 6 to 10 of the Periodic Table, in the case of manganese for example with Mn(NO3)2, MnSO4, MnHPO4, MnCO3 or MnCl2, the latter being employed in optionally dilute sulfuric, nitric or phosphoric acid. Drying and calcination are then carried out.
The procedure for preparing catalysts based on zirconium oxide (and analogously for the other metal oxides) which are doped with P can, for example, be to suspend commercially available zirconium oxide and/or zirconium hydroxide in water, bring the suspension into contact with dilute phosphoric acid or an aqueous ammonium phosphate solution, remove the water, for example by distillation under reduced pressure, and dry the residue. The crude catalyst composition obtainable in this way can be either directly calcined or further processed to shaped articles and then calcined. It is also possible for the drying step to be followed by another impregnation step with an aqueous solution of a salt of a metal of groups 6 to 10, for example a manganese salt.
The calcination is normally carried at from 500 to 900xc2x0 C., preferably at about 700xc2x0 C. in 5 to 25 hours, preferably 10 to 20 hours. During this there is conversion, for example, of HPO42xe2x88x92 or H2PO4xe2x88x92 into P2O74xe2x88x92 and other cyclic phosphates and of HCO3xe2x88x92 into CO32xe2x88x92. However, this conversion preferably does not take place completely under the chosen conditions so that, for example on use of P, there is still PO43xe2x88x92 remaining in the resulting catalyst.
The Zr contents of the individual catalysts, determined by X-ray fluorescence analysis (R. Bock: Methoden der analytischen Chemie, Bd. 2, Nachweis- und Bestimmungsmethoden Teil 1, Verlag Chemie, Weinheim 1980), are between 60 and 71 g, preferably between 65 and 70 g, per 100 g of catalyst. The P, S and Mn contents are determined by ICP (Inductively Coupled Plasma) atomic emission spectroscopy (A. Montasa, D. W. Golightly: Inductively Coupled Plasmas in Analytical Atomic Spectrometry, 2nd edition, Verlag Chemie, Weinheim). Typical values are P: 0.2 to 1 g/100 g; S: 0.1 to 1 g/100 g and Mn: 0.1 bis 5 g/100 g of catalyst.
Normally used in the novel process are amino nitriles of the formula II:
R1HNxe2x80x94Xxe2x80x94CNxe2x80x83xe2x80x83(II)
in which X is an alkylene unit having at least 2 and at most 20 atoms. As a rule, these are carbon atoms, but there may also be one or more, but preferably not more than three, boron, nitrogen, phosphorus, oxygen and/or sulfur atoms present at any position within the alkylene unit. Between the amino group of the general formula xe2x80x94NR1H and the nitrile group there are at least 2, and preferably 3 to 6, atoms, preferably carbon atoms. Examples of alkylene are ethylene, 1,2- and 1,3-propylene, 1,2-, 1,3-, 1,4-, 2,3-butylene and 2-methyl-1,3-propylene, 1,2-, 1,3-, 1,4-, 1,5-, 2,3-, 2,4-pentylene, 2-ethyl-1,3-propylene, 2,2-dimethyl-1,3-propylene and 2- or 3-methyl-1,4-butylene, 1,2-, 1,3-, 1,4-, 1,5- and 1,6-hexylene, 2-, 3- or 4-methyl-1,5-pentylene, 2,2- or 2,3-dimethyl-1,4-butylene, 2- or 3-ethyl-1,4-butylene, 2-ethyl-2-methyl-1,3-propylene and 2-propyl-1,3-propylene, 3-oxa- and 3-thia-1,5-pentylene. R1 is hydrogen or a straight-chain or branched alkyl group having up to 20 carbon atoms. Examples of suitable alkyl groups are methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, n-pentyl, n-hexyl and 2-ethylhexyl. Amino nitriles with linear alkylene units X with 3, 4, 5 or 6 carbon atoms and primary amino groups are preferably used, i.e. 4-aminobutyronitrile, 5-aminovaleronitrile, xcex5-aminocapronitrile and 7-aminoenanthonitrile, particularly preferably xcex5-amino-capronitrile. The ratio of water to amino nitrile can be in the range from 1 to 50 mol/mol, preferably from 1 to 15 mol/mol.
The reaction can be carried out either in an agitated or in a stationary catalyst bed. The gas-phase reaction is preferably carried out on a fixed bed. The fixed bed can be arranged, for example, as a single bed or else divided over several trays. In the latter case, it is possible to influence the composition and the physical properties of the reaction mixture between the trays in a beneficial manner, for example by adding reactants or inert gases or using, for example, heat exchangers. The fixed bed may additionally be arranged in one or more reaction chambers, e.g. in a tube bundle reactor.
The reaction temperature will usually be in the range from 200 to 550xc2x0 C., preferably from 300 to 400xc2x0 C. A temperature which is too low would make the evaporation of the starting material difficult, and, in addition, high conversions can be achieved only with difficulty under these conditions. If the temperatures are too high there is increased formation of byproducts and decomposition products.
The pressure can be in the range from 0.01 to 10 bar during the reaction. The reaction is preferably carried out under atmospheric pressure.
The reaction can also be carried out with the addition of inert gas, for example argon or nitrogen. The molar ratio of inert gas to amino nitrile can be, where appropriate, in the range from 0 to 100 mol/mol.
The discharge from the reactor usually contains not only the lactam as product but also unreacted amino nitrile and water, and ammonia or amine and, in small amounts, byproducts such as amino carboxamides. The lactam can be isolated therefrom in a manner known per se, for example by distillation, extraction or crystallization.
Typically, from 50 to 2000 g, preferably more than 500 g, of amino nitrile/l of catalyst and hour are fed into the reactor. The amino nitrile conversions are then in the range from 70 to 99.9%. The selectivity for lactam formation is, as a rule, above 85% based on amino nitrile employed. Selectivities achieved with preferred catalysts are also xe2x89xa790% and, in particular, xe2x89xa793%. These figures are even reached after the catalyst has been in use for several hundred hours.